1. Field of the Invention
The invention relates to catalysts based on amorphous partially dehydrated zirconium hydroxide (ZrO.sub.2.xcH.sub.2 O), a process for their preparation and also their use in hydrogen transfer reactions between carbonyl compounds and alcohols, in particular the Meerwein-Ponndorf-Verley reduction and the Oppenauer oxidation. The invention further relates to a process for preparing 3-hydroxyquinuclidine of the formula: ##STR2## by reduction of quinuclidin-3-one of the formula: ##STR3##
2. Background Art
It is known that the hydrogen transfer reactions between aldehydes or ketones and primary or secondary alcohols which are usually carried out under the catalytic action of aluminum alkoxides and summarized under the names "Meerwein-Ponndorf-Verley reduction" and "Oppenauer oxidation" can also be carried out under heterogeneous catalysis [C. F. de Graauw et al., Synthesis, (1994), 1007-1017]. Owing to the easier work-up of the reaction mixture and the fact that the catalyst may possibly be reused, this variant is of great interest. As the heterogeneous catalyst, use has been made, inter alia, of partially dehydrated zirconium hydroxide (hydrous zirconium oxide) [M. Shibagaki et al., Bull. Chem. Soc. Jpn., (1988), 61, 3283-3288; Bull. Chem. Soc. Jpn., (1988), 61, 4153-4154; and Bull. Chem. Soc. Jpn., (1990), 63, 258-259; and H. Kuno et al., Bull. Chem. Soc. Jpn., (1990), 63, 1943-1946; and Bull. Chem. Soc. Jpn., (1991), 63, 312-314]. However, the activity of this catalyst is not very high, so that, particularly when using relatively unreactive carbonyl compounds and/or alcohols, only moderate or poor yields are frequently obtained.
3-Hydroxyquinuclidine is a starting material for the synthesis of various pharmaceutically active compounds such as choline mimetics (U.S. Pat. No. 2,648,667, and European Published Patent Application No. 0370415) or bronchodilators (WO-A-93/06,098). Various methods are known for preparing 3-hydroxyquinuclidine from quinuclidin-3-one (U.S. Pat. No. 2,648,667), namely, the hydrogenation of the hydrochloride using platinum oxide as the catalyst, the reduction of the hydrochloride using sodium/ethanol, the hydrogenation of the free base using platinum oxide or Raney nickel as the catalyst, and also the reduction of the free base with lithium aluminum hydride. However, none of these methods is free of disadvantages. Platinum oxide is very expensive, Raney nickel is pyrophoric and both sodium/ethanol and lithium aluminum hydride as reducing agent lead to safety and waste problems when employed on an industrial scale.